东亚夏季风和中国雨季的趋势变化和关键区气温和海温的影响

中国降水主要受到西风和季风环流的共同影响,表现出显著的年循环特征。本文基于1961~2020年CN05.1逐日降水资料和JRA55、CRU、HadISST再分析资料,采用谐波分析、相关和回归统计方法,分析了过去60年的东亚夏季风(中国雨季)的建立(开始)、撤退(结束)和持续时间等年循环参数趋势的变化特征。结果显示,自1961年以来,东亚夏季风有建立时间提前,撤退时间推后,持续时间增长的趋势,每十年分别达到了3.54、1.64、5.18天。1999年前后22年我国雨季也存在趋势变化,且在空间上存在显著差异。最近22年(1999~2020年),我国雨季提前主要集中在东北东部、青藏高原东部、西北北部地区,提前时间达5天以上,部分地区超过了20天。雨季滞后主要集中在青藏高原东北,长江以北和西部地区,时间超过了10天。雨季持续时间增加主要集中在青藏高原东北部、我国长江以北、东北东南部地区,时间超过15天以上,部分地区超过25天。研究发现,4月份环贝加尔湖地表气温增加及其伴随的局地反气旋性环流异常,是东亚夏季风建立和我国雨季开始时间提前的关键,而10月份的西北太平洋海温增暖及其伴随的西北太平洋副热带反气旋的异常是导致东亚夏季风撤退和中国北方雨季变长的关键。

2007—2021年上海莘庄太阳最大入射辐射变化特征和环流背景

利用2007—2021年上海莘庄太阳能辐射仪(型号:EKO-MS6020)接收到的逐月最大太阳辐射(MSR)资料,以水平0°角辐射仪观测值为参考,分析了0°—25°不同仰角观测的MSR差异,评估了台站观测、欧洲中期天气预报中心(ECMWF)大气再分析(ERA5)资料与太阳能辐射仪观测辐射的差别。在此基础上,讨论了MSR与天气要素的关系及发生的环流背景和天气尺度演变特征。结果显示,上海莘庄的MSR季节波动范围为800—1300 W/m^(2),峰值和谷值分别出现在5月和12月。观测的最大MSR值接近太阳常数,年际变化幅度约200 W/m^(2)。相对于0°角观测,当太阳能板倾角为5°—20°时,平均每个月MSR可多获得50—250 W/m^(2)辐射,最佳倾角为20°。ERA5相对于观测MSR存在明显低估,年平均低估约200 W/m^(2)。虽然两者的季节变化相关系数高达0.88,但是在空间和时间上存在显著差异,年际变化相关并不显著。针对与MSR时间相差小于3 d的大气环流背景合成,春、夏、秋、冬四季的环流结构存在差异,但总体来看,偏北风加强、云量偏少、温度偏高的天气过程有利于MSR出现。

东亚夏季风次季节变化研究进展

东亚夏季风次季节(10~90d)变化是中国夏季持续性强降水、高温热浪等高影响天气事件的重要环流载体,处于天气预报上限和气候季节预测下限之间的预报过渡区。研究表明:东亚夏季风次季节变化是东亚夏季风的固有物理特征,它和季节进程之间的时间锁相关系是东亚夏季风次季节变化潜在可预报性的重要来源。东亚夏季风次季节变化与Madden-Julian振荡(MJO)存在显著差异,试图通过MJO来预测东亚夏季风次季节变化的不确定性较大。东亚夏季风次季节预测的另一重要来源是下垫面外强迫,包括欧亚大陆春季积雪、中国东部春季土壤湿度和厄尔尼诺-南方涛动(ENSO)事件。此外,去趋势偏-交叉相关分析统计方法能够分析东亚夏季风多因子和多时间尺度问题。目前,亟需解决的科学问题包括:东亚夏季风次季节模态的客观定量描述、造成东亚夏季风次季节模态年际变化的关键物理过程、不同外强迫因子对东亚夏季风次季节模态的共同影响。

气候动力诊断和分析系统设计与应用

气候动力诊断和数值模拟是认识气候变化规律、提高短期气候预测与科学决策服务水平的重要手段。但基于气候模拟的动力诊断技术在气候预测业务中还未得到广泛应用,缺乏支撑科研成果转化为业务应用的中试平台。为此,通过集成多种现代计算机通信协议、可视化编辑和气象数值计算等技术,研发可视化交互气候动力诊断和分析系统(Climate Dynamic Diagnosis and Analysis System,CDDAS),以促进气候模拟的动力诊断技术在气候业务中的广泛应用。该系统具有结构开放、诊断方法集成度高、方便易用等特点,包括数据更新备份、气候动力诊断、多模式数值模拟、结果分析4个功能模块,并设计了一种远程交互控制脚本语言,为用户二次开发提供语言环境,可实现本地客户端、服务器端和超级计算机三者交互通信控制可视化管理。该系统使用便捷,目前已在国家级业务和科研单位获得应用,在气候异常成因分析、气候预测和气候决策服务中可显著提高工作效率。

东亚夏季环流多齿轮耦合特征及其对中国夏季降水异常的影响分析

东亚夏季风成员的相互作用,构成了东亚夏季风高、低层环流的"多齿轮耦合"形态。本文利用多变量主成分分析(MV-EOF)等方法诊断分析了东亚夏季风多齿轮耦合的变化特征、耦合机制、时间稳定性、空间稳定特征及其对中国夏季降水的影响机制,并在此基础上构建了典型多齿轮耦合形态影响夏季降水的概念模型。结果表明,多齿轮耦合受到垂直温、压场的强迫和青藏高原大地形的影响,主要表现在年际变化上(周期为2~6年)。其前两个模态稳定地反映了东亚夏季风成员典型联动作用。在第一模态中,北方气旋、南亚高压和西太平洋副热带高压为主要耦合系统。其中北方气旋为正压结构,在高层通过南侧偏西气流与南亚高压耦合,南亚高压则通过中纬东部地区下沉辐散气流与西太平洋副热带高压联动。当该耦合模态增强时,有利于中国夏季降水呈自北向南"+-+-"分布。第二模态主要反映中高纬气旋、东亚副热带西风气流、南亚高压、西北太平洋反气旋系统和西太平洋副热带高压耦合特征。其中,中高纬气旋和西北太平洋反气旋为正压系统,两者通过其间的东南气流联动。气旋系统在高层通过南侧西风与东亚副热带西风急流和南亚高压联动。反气旋在中低层通过南侧的偏东气流影响副热带高压强度和面积。当该耦合模态增强时,中国黄河以北及河套地区降水偏多,黄河以南降水偏少。

西南夏季降水多因子降维客观预测方法研究

本文改进了现有的多模态时间稳定性判别标准,提出一种筛选稳定高相关预测信号的思路,对1981~2016年西南夏季降水距平百分率多模态的时间稳定性、时空特征和可预测模态关键信号等进行了分析研究,在此基础上构建了多因子降维预测模型。结果表明,前9个模态在预测时效为3年和近10年内稳定,累计方差贡献率占70%,是西南夏季降水的主要模态。结合稳定高相关概念和最优子集回归方法得到主模态PC(Principal Component)系数的最优预测信号和预测方程。回报检验结果表明,各方程对PC系数有较好的拟合效果,复相关系数为0.62~0.84,均通过了99.99%的显著性检验,同号率均大于69%。构建的多因子降维预测模型对西南夏季降水的空间分布,正负趋势和异常级有较好的回报效果:距平相关系数(Anomaly Correlation Coefficient,简称ACC)平均值为0.58;时间相关系数(Temporal Correlation Coefficient,简称TCC)在除零星站点外的整个区域通过90%的显著性检验,且大部分区域通过99.9%的显著性检验;趋势异常综合评分(PS)平均分为84,其中区域降水最异常的十年,PS平均分为87.1。经过13年(1971~1980年和2017~2019年)的预报检验,该模型的PS平均分为72。其中2017~2019年的PS均分为77,优于发布预测评分。

2019年4~6月云南持续性高温天气的大气环流异常成因

2019年4~6月云南省发生了历史罕见的持续性极端高温天气,并引发了严重气象干旱。本文利用1961~2019年逐日温度和大气再分析等资料以及CESM-LE计划(Community Earth System Model Large Ensemble Project)模式模拟结果,分析了历史同期云南极端高温天气发生的环流特征,探讨了2019年云南破纪录持续性高温的成因。历史极端高温日的合成分析表明,云南地区对流层上层显著异常反气旋伴随的强下沉异常和到达地表太阳辐射增加,是引发该区域极端高温天气的主要成因。该异常反气旋的形成主要源自北大西洋经东欧平原、西西伯利亚平原向东亚传播的高纬度罗斯贝波和经北非、黑海、伊朗高原向东亚传播的中纬度罗斯贝波之间的相互作用。2019年极端高温的强度和与之相应异常反气旋出现自1961年以来的最强。外强迫导致的增暖对2019年极端暖异常强度的贡献约为37.51%,同时对类似2019年以及更强极端暖事件发生概率的贡献为56.32%,内部变率对该事件也具有重要贡献。2019年4~6月北极涛动(Arctic Oscillation,AO)和ENSO事件分别处于历史极端负位相和暖位相。一方面,在AO强负位相影响下,极地上空深厚的位势高度正异常向南伸至东欧平原,有利于高纬度波列和云南上空的反气旋异常增强。另一方面,ENSO事件暖位相加强了西北太平洋异常反气旋环流,令西北太平洋副热带高压增强西伸至我国内陆地区,维持了云南上空反气旋异常。两者的共同作用,造成了2019年4~6月云南上空持续的深厚异常反气旋,云南地区继而出现持续性极端高温事件。

The Natural Oscillation of Two Types of ENSO Events Based on Analyses of CMIP5 Model Control Runs

The eastern-and central-Pacific El Ni（n）o-Southem Oscillation （EP-and CP-ENSO） have been found to be dominant in the tropical Pacific Ocean,and are characterized by interannual and decadal oscillation,respectively.In the present study,we defined the EP-and CP-ENSO modes by singular value decomposition （SVD） between SST and sea level pressure （SLP） anomalous fields.We evaluated the natural features of these two types of ENSO modes as simulated by the pre-industrial control runs of 20 models involved in phase five of the Coupled Model Intercomparison Project （CMIP5）.The results suggested that all the models show good skill in simulating the SST and SLP anomaly dipolar structures for the EP-ENSO mode,but only 12 exhibit good performance in simulating the tripolar CP-ENSO modes.Wavelet analysis suggested that the ensemble principal components in these 12 models exhibit an interannual and multi-decadal oscillation related to the EP-and CP-ENSO,respectively.Since there are no changes in external forcing in the pre-industrial control runs,such a result implies that the decadal oscillation of CP-ENSO is possibly a result of natural climate variability rather than external forcing.

东亚季风年循环和位相异常导致的降水年际变化特征

基于1979-2016年资料分析,本文发现,东亚季风可以分解为春分和夏至两个模态,分别反映的是春夏和秋冬影响我国华南和大陆的环流降水特征。东亚夏季风的季节进程表现为春分模态向夏至模态的演变。在年际尺度上,春分和夏至模态的时间位相变化表现出显著的正相关,前冬的ENSO和西北太平洋海温变化可导致东亚季风年循环年际异常,进而造成华南和华北部分地区的冬夏和春秋降水隔季反向变化,这为我国跨季节的降水气候预测提供了理论依据。

中国华南地区冬季冷湿气候次季节模态（英文）

本文研究了中国冬季气温和降水的气候次季节(CISO)主模态特征,并讨论了华南地区冷湿模态与极地环流的次季节尺度变化关系。结果发现,在CISO正位相时,冬季的华北和华南分别表现为冷干和冷湿模态,在时间上表现为准30天周期振荡特征。其中,华南的气温次季节波动在冷湿模态起主导作用。在北极涛动负位相下,500-hPa位势高度的次季节尺度波动表现出向南传播特征,由此导致冷锋南下和降温。局地冷性气旋波活动增强了西伯利亚高压的不断南下,有利于大气的不稳定,进而造成华南地区的冷湿气候。因此,冷空气活动可以作用华南次季节降水预测的前兆因子。

Linkage between the dominant modes in Pacific subsurface ocean temperature and the two type ENSO events

We investigate the variations of subsurface ocean temperature(SOT) based on the monthly-Simple Ocean Data Assimilation(SODA) during 1958-2007,and discuss the linkage between the variations of SOT and the eastern and central Pacific ENSO(EP and CP-ENSO) events.The wavelet analyses suggest that the variation of the EP and CP-ENSO events shows the 2-7 and the 10-15 years oscillation in the tropical sea surface temperature(SST),and coupled with a zonal dipole mode and a tripole mode in the SOT anomalous field reveled by the singular value decomposition(SVD) analysis.During the mature phase of CP-ENSO,the positive center of SOT at the subsurface layer locates in the west of dateline,which results in the increase of SOT in the Ni o4 region and causes the CP-ENSO event.Statistical analysis implies that,the eastern and central Pacific subsurface indices which are defined by the expansion coefficients of the first and third SVD mode for SOT have shown the capabilities in disguising the EP and CP-ENSO events,respectively.In addition,corresponding to the increase of the SOT amplitude on the 10-15 years time scale,we found that the frequency and intensity of CP-El Ni o events has exhibited an upward trend after the 1980s,which suggests that the CP-ENSO event has shown an enhanced impact on the global climate in the past decades.

How would global-mean temperature change in the 21st century?

The time series of HadCRUT3 global-mean surface air temperature(GSAT) anomaly,Pacific decadal oscillation(PDO) index,and the equatorial Pacific sea surface temperature(SST) were utilized,and their long-term trends and multiple time-scale periodic oscillations were explored in this study.A long-term trend with a warming rate about 0.44°C /century during 1850-2008,two cool floors occurred respectively around 1910 and during 1950-1970,and three warm flats happened in the 1870s,1940s and since the year 1998 were found in the GSAT.In this duration,the variability of GSAT can be well reconstructed by the quasi-21-year,the quasi-65-year,and century-scale oscillations.The recent decadal warm flat is caused by their positive phase overlapping from these three oscillations.The maximum rising temperature reached 0.26°C was simulated in 2004 by the three oscillations.The quasi-21-year and the quasi-65-year oscillations were possibly caused by solar radiation and internal variability of the ocean-atmosphere system.Therefore,an outlook of GSAT for the 21st century was made based on the long-term trend and these three oscillations.It was expected that a cool floor and a warm flat of the GSAT would appear in the 2030s and 2060s,respectively.However,the highest warming range is predicted about 0.6°C,it is less than the threshold 2°C and IPCC projection.

Onset of East Asian subtropical summer monsoon and rainy season in China

Here we use harmonic analyses to examine seasonal variations of China land rainfall, low-level winds, and atmospheric heating over East Asia during spring to summer and the associated subtropical summer monsoon activities. Our results indicate that the South China spring rainfall (SCSR) in March is the prophase of East Asian sub-tropical summer monsoon (EASSM), and the onset of EASSM and China summer rainy season starts in early April, characterized by the enhanced rainfall in South China and the seasonal reverse of zonal land-sea thermal contrast in sub-tropical East Asia. The EASSM onset is earlier than that of South China Sea summer monsoon, and it is active in east of 100?E and north of 20?N. Our analyses suggest that the subsequent heating appears over India-China Peninsula in March and South China in April and causes the low-level atmospheric warming and the zonal land-sea thermal contrast seasonal reverse in East Asian subtropics. The atmospheric heating over South China is the main force to drive the southwesterly winds, updrafts and strengthen the summer precipitation in South China.

Modeling impacts of East Asian Ocean-Land thermal contrast on spring southwesterly winds and rainfall in eastern China

Using the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis dataset, the NOAA’s Climate Prediction Center’s merged analysis of precipitation, and the MM5v3 Meso-scale Model, the impacts of surface temperature differences between the East Asian land and its adjacent oceans on spring southwesterly winds and rainfall over eastern China are studied. The modeling results show that the temperature differences exert strong influence on the occurrence of the southwesterly winds and rainfall over southern China and their northward advances. When surface temperature increases over the land and decreases over the oceans, the temperature gradient with a winter feature earlier changes toward the gradient with a summer feature. Both the low-pressure system east of the Tibetan Plateau and the subtropical high-pressure system over the western Pacific strengthen, accompanying with the strengthening of the lower-tropospheric southwesterly winds over eastern China. Accordingly, the upward motion increases over the Yangtze-Huaihe River (YHR) valleys and decreases over southern China, leading to an increase of spring rainfall over the YHR valleys and a decrease over southern China. Thus, the rain belt over eastern China appears over the YHR valleys but not over southern China. Under a weaker condition of the spring thermal contrast, the rain belt does not occur over eastern China. When the spring thermal contrast pronouncedly strengthens, the rain belt over southern China may advance northward into the YHR valleys during spring, though there is no onset of the tropical monsoon over the South China Sea. This forms a rain belt similar to that of the YHR valleys during the summer Meiyu period.

Decadal change of the East Asian summer monsoon and its related surface temperature in Asia-Pacific during 1880–2004

The East Asian summer monsoon(EASM)and its related change of surface temperature in the past century were not clearly addressed due to absence of atmospheric reanalysis data before 1948.On the benchmark of station-observed sea level pressure(SLP)in China,we utilized multiple SLP datasets and evaluated their qualities in measuring the SLP-based EASM index(EASMI).It is found that the EASMI based on the SLP of the Hadley center version 2(HadSLP2)has shown the best performance on the interannual and decadal time scales.Instead of showing a linear weakening trend pointed out by the previous study,the EASMI has likely exhibited the decadal variability,characterized by weakened trends during 1880–1906,1921–1936,and 1960–2004,and with enhanced trends during 1906–1921 and 1936–1960,respectively.Corresponding to the weakened and enhanced periods of EASMI since the 1920s,the surface air temperature(SAT)index(SATI)averaged in eastern China has likely shown a warming and a cooling trend,respectively.However,the decadal abrupt transitions between the two indices do not occur concurrently,which results in a weak correlation between two indices on the decadal time scale.Further analysis indicates that there are four key regions where the SAT is significantly correlated with the EASMI,suggesting the joint impact of surface temperature in Asia-Pacific on the EASM during 1880–2004.In which,the decadal change of SAT near the Lake Baikal plays an important role in the linear trends of the EASM before and after 1960.